As photocurable organic polymer compositions can be quickly cured under the effect of light radiation such as infrared rays or electron beams, they find wide application as coating agents for parts of electronic devices. For example, Japanese Laid-Open Patent Application Publication (hereinafter referred to as “Kokai”) S61-127718 (U.S. Pat. No. 4,528,081) describes a curable moisture-penetration-resistant polyorganosiloxane composition which consists of a silicone oil having a trimethylsilyl terminal group, a photosensitizer, and a reactive polyorganosiloxane which contains a condensation-reaction catalyst. The aforementioned reactive polyorganosiloxane is obtained as a result of a reaction between a silanol-capped polyorganosiloxane and an acryl-trialkoxysilane or an acryl-triallyloxysilane in the presence of said catalyst. The aforementioned reaction results in the formation of acryldialkoxysilyl or acryldiallyloxysilyl terminal groups. Furthermore, Kokai H6-32985 (U.S. Pat. No. 5,371,116) describes a curable polyorganosiloxane composition which is characterized by photocurable and moisture-resistant properties and consists of a silanol-capped polyorganosiloxane, methacryl-functional alkoxysilane, a tin-type compound, alkoxy-α-silyl ester, a photoinitiator, and a curing catalyst.
However, in a cured state the aforementioned optically-curable polyorganosiloxane composition is not able to provide sufficient resistance to moisture, and therefore when electronic parts having coatings made of such compositions are used in a humid environment, their electroconductive elements are subject to corrosion.
It is also known to make coatings of electronic parts from photocurable organic polymer compositions that contain adhesion promoters of an alkoxysilane type, but such agents have low adhesiveness and cannot provide sufficient protection of electronic parts from corrosion.